Various known writing utensils have a fibrous writing tip, or nib, and a reservoir filled with liquid ink in communication with the nib. In general, these writing utensils, e.g., markers and pens, include a separate cap that releasably attaches to the body of the writing utensil to cover and seal the nib in a substantially air-tight manner. In this way, the liquid ink disposed in the nib and the reservoir does not evaporate, and the writing utensil does not dry out. While the cap is successful in keeping a tight seal over the nib and keeping the writing utensil functional, the writing utensil will inevitably dry out and be ruined if the cap is lost.
To address this issue, the so-called “cap-less” maker has been devised. In certain cap-less markers, the nib is retractable from an extended writing position, in which the user can write with the marker, to a retracted or withdrawn position, in which the nib is stored in a valve. The valve generally includes a valve door which substantially seals the nib inside the valve when the marker is in the retracted position. The valve door opens up to allow the nib to extend out of the body of the marker into the writing position so the user can write with the marker.
U.S. Pat. No. 5,048,990 to Hashimoto describes a cap-less marker that has been successfully commercialized. In the commercialized version of this marker, the nib is a large fiber-type tip, and the valve is made entirely from a thermoplastic elastomer, also known as TPE. While a TPE valve can generally provide a good seal between the valve body and the valve door, many TPE's have poor vapor barrier properties. Thus, solvent vapor from the ink is likely to permeate through the walls of the valve so as to dry out the nib/tip. Further, all-TPE valves may exhibit poor structural integrity over time. For example, the commercialized Hashimoto valve is subject to loading applied by a spring and a string when the writing tip/nib is in the retracted (or sealed) position. Over time, the TPE material begins to creep and the valve deforms. This deformation can inhibit the valve's ability to maintain an air-tight seal between the valve body and the valve door.
In the case of a marker including a (relatively) large, fibrous nib; a valve made from TPE generally works adequately. In such markers, the large nib retains a large volume of ink and has a relatively large wick portion in fluid communication with an ink reservoir. The wick portion includes many capillary channels, which allows a large volume of ink to travel from the reservoir to the writing tip. Thus, the nib can generally replenish any ink within the nib/tip that evaporates so that the nib does not dry out, and the writing utensil is not ruined. However, consumers are demanding permanent markers with an ultra-fine tip, instead of a large fiber-type tip, for everyday writing. Such a marker has a much smaller nib/tip made from an extruded plastic, includes very small capillary channels, and has a smaller wick portion in fluid communication with an ink reservoir.
An all-TPE valve is generally not satisfactory for an ultra-fine tip due to ink vapor permeating through the valve walls. An ultra-fine tip has very small capillary channels where very little ink is present. Because only a small amount of ink permeation or evaporation will clog the tip, this construction is vulnerable to ‘hard starting,’ and susceptible to complete dry-out. Hard start means the marker struggles to write initially with little or no ink being deposited on the paper. Consequently, dry-out is of greater concern for such ultra-fine markers (relative to markers including a large, fibrous nib/tip).
While the devices and methods described herein are susceptible to various modifications and alternative constructions, certain illustrative embodiments have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed. On the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the disclosure.